Detector circuits



Nov. 29, 1938. l R H, CRAlG 2,138,731

DETECTOR C IRCUI TS Filed Feb. '28, 1955 vPatented Nov. 29, 1938 UNITED STATES DETECTOR CIRCUITS Palmer Hunt Craig, Bethlehem, Pa., assignor to Invex Corporation, New York, N. Y., a corporation of New York Application February 28, 1935, Serial No. 8,741

11 Claims.

My invention relates to electric circuits for detecting the presence or proximity of conducting bodies. The circuits of my invention may be employed in burglar alarm systems, trailic counting systems, and in manufacturing processes where it is desired to detect the presence of a conducting body in a certain locality. One form of my invention may also be used for determining the weight of objects.

This application is in part a continuation of application Serial No. 688,249, led September 5, 1933, Patent No. 2,001,838, and also contains subject matter disclosed in my copending applicaions Serial Nos. 577,691, Patent No. 2,001,836, led November 27, 1931, and 646,662, Patent No. 2,001,837, led December 10, 1932.

Figures 1 to 3 of the accompanying drawing are diagrams of detector circuits taken from my application Serial No. 688,249;

Figures 4, 5, 6, 8 and 9 are diagrams of circuits taken from my application Serial No. 577,691; and

Figure 7 is a diagram of a circuit taken from my application 646,662.

My invention involves the use of a gaseous relay tube having an electron emitting cathode, an anode and a grid or control electrode. In one form of gaseous relay the control element is located within the envelope or tube in the space between the cathode and the anode, and in another form, the control or grid element is located outside of the envelope, usually at a point lying being the cathode and the anode. I prefer to use the second form of gaseous relay, that is, the type with the external grid, but the internal grid type may be used, if desired.

Referring to Figure l, relay tube I is formed of a glass bulb provided with an electron emitting cathode 2, an anode 3, and an external grid or control electrode 4. The tube I is also provided with a gaseous atmosphere such as mercury vapor neon, xenon, or other suitable ionizable gas or vapor. The relay tube may consist of a type 866 hot-cathode mercury vapor rectifier described in Q. S. T. for February, 1929, pages 20 to 22, and provided with an external grid. `Various forms of relay tubes are also illustrated in Electronics for March, 1933, pages 70 to 72. The cathode 2 is heated from a low voltage winding 5 of a transformer T, the primary winding of which is connected across the terminals of an alternating current source 6 1. A suitable alarm I6, or an indicating device I 6a, is connected in a circuit across the terminals 6-1 in series with the anode-cathode elements of the tube I. One terminal of high voltage winding 9 of transformer T is connected to the cathode heating circuit by condenser I I, and the other terminal is connected to grid 4 by variable condenser I2. The polarity of winding 9 is such that when the anode3 is positive with respect to the cathode 2, the grid 4 is negative with respect to the cathode. A Variable resistance I1 may be included in the anode circuit, if desired, for limiting the anode current. Since the potential impressed upon the grid 4 by the condenser I2 is opposite in phase to the anode potential, the grid 4 exerts a restraining influence upon the arc in the relay I, and by varying the value of condenser I2, (or of condenser II) the starting of the arc in the tube may be controlled. It will be understood that increasing the value of the condenser increases the potenial applied to the grid and thereby decreases the elective value of the anode current.

The circuit of Figure 1 is quite sensitive to capacity variations produced in the grid circuit by conducting bodies near the grid circuit, especially when the grid potential is adjusted to the critical value where the anode current is just prevented from starting. In order to make the circuit more sensitive for detecting the presence of conducting bodies, a conducting grid or plate I8 is connected to the grid 4 and is arranged in the locality to be protected against burglars. When the condenser I2 is adjusted so that the arc within the tube I is just prevented from forming, the approach of a person or any conducting body within the vicinity of the plate I8 will reduce the control potential applied to the grid 4 and permit the arc to be established, thereby energizing the signal I6. It will be obvious that the condenser II may be omitted, and the lower terminal of winding 9 connected directly to the cathode circuit.

The arrangements described above may be employed for the purpose of detecting the passage of persons or objects along a passageway by placing the capacity plate I8 at a point along the passageway so that the body or object to be detected passes near the plate. The variation in the anode current caused by the passage of such. persons or objectsmay be utilized through well known means for indicating or recording the number of passages taking place, or for indicating the presence of an object at a certain point in the passageway. The indicating device may be located at a point remote from the control tube. Furthermore, with the arrangement shown and with proper adjustment of condensers I I and I2, it is possible by an indicating meter Ilia to obtain an indication of the nearness or proximity of the object with respect to the plate I8. However, for greatest sensitivity in detecting the presence of objects, the adjustment will be such that the operation of the tube is substantially on-and-off. The arrangement of Figure 1 may be modied by omitting the plate I8 and by forming the variable condenser I2 of plates of suitable size arranged on opposite sides of a passageway as indicated in Figure 2. The condenser 4plates are indicated at I2a and I2b, and the object to be detected is indicated at I9 between the plates. With this modication, the tube is normally inactive, but the passage of an object between the plates of the condenser causes the arc in the tube to strike, and the resulting current operates the signal or recording device I6. It is obvious that instead of connecting the grid control circuit to a point on the cathode heating circuit, this circuit may be connected to the anode lead or to any point on the anode-cathode circuit. This modied connection may be embodied in any oi' the detector circuits of this application, and is obtained in Figure 2 by the use of switch 22, but it will be understood that the connection may be made directly to the anode without the use of the switch. v

In the operation of Figure 2, the tube would be normally conducting, and the passage of the body or object I 9 between the condenser plates will cause an increase in the restraining potential applied to the grid and will reduce the eective value of the anode current ilowing in the circuit.

Figure 3 illustrates a third detector circuit somewhat like Figure 1. In this arrangement, the condensers II and I2 are omitted, and a potentiometer comprising a resistance I Il and a variable contact Illa is employed for the purpose of adjusting the restraining potential applied to the grid. The action of this circuit is substantially like that of the circuit in Figure l, except that more oi' a trigger-like action is obtained than in the circuit of Figure l, due to the operation which results in the abrupt establishment and the cutting-off of the anode current for slight variations below and above a critical value of the control voltage.

The arrangement shown in Figure 4 is taken from my copending application Serial No. 577,691, and also disclosed in my application Ser. No. 646,662. This circuit embodies features disclosed in both Figures 2 and 3, and corresponding elements are indicated by corresponding reference numerals. The condenser 8 connected in series with resistance I0 is for the purpose of fixing the phase of the grid or control potential so that it lags the anode potential by an angle of the order of 135 degrees for the purpose of giving a more uniform control of the anode current by variation of the contact IIla as more fully disclosed in my copending application Serial No. 577,691. The operation of this circuit is like that of Figure 2, since the presence of the conducting body I9 between the plates of the grid condenser causes a decrease in the anode current and produces a corresponding operationof the indicating or recording device IG. As previously disclosed in my application Ser. No. 646,662, the grid circuit return may be connected to the anode circuit instead of the cathode circuit.

The circuit arrangement shown in Figure 5, previously disclosed in my application Serial No. 577,691 involves the use of an additional grid 4a on the tube I. This circuit is somewhat like the circuit shown in Figure 4, except that the condenser I2 is connected between the second grid 4a and the cathode circuit. In the operation of this circuit, the potential applied to the grid 4 exerts a restraining influence upon the anode current, and the passage of a conducting body I8 between the plates of the condenser I2. reduces or impairs the restraining action of the grid 4 and causes a greater anode current to flow which is either recorded or indicated by the device I 6.

The circuit shown in Figure 6 is like the circuit of Figure 4 and diiIers therefrom in that the detecting condenser I2 is connected between the grid 4 and the cathode circuit, and a small condenser I3 is inserted between the variable tap on resistance I l and the grid 4. This condenser may be omitted if desired. This circuit operates in substantially the same manner as Figures 1 and 3, except that due to the particular phase displacement between the control voltage and the anode voltage, a more uniform variation of the anode current is obtained than in Figures 1 and 3.

Figure 7 is a composite circuit diagram illustrating circuits originally disclosed in my application Ser. No. 646,662. This circuit differs from Figure 1 in that the phase determining elements 8 and I0 are connected across the secondary winding 9, and the capacity element Ila is shown as a. short length of wire. The return for the grid circuit may be connected either to the cathode circuit or to the anode lead, and for the sake of convenience, these two modiilcations have been illustrated by means of the switch 22. The wire I8 is arranged so that the object to be detected comes near the wire, and the presence of the object reduces the potential upon the grid and causes an increase in the anode current.

Figure 8 is a modiiication of the circuit diagram shown in Figure 4. In this arrangement, the anode current for the tube issupplied from a secondary winding 9a instead of directly from the alternating current terminal 6-1 as in Figure 4. It is obvious that an additional secondary winding corresponding to winding 9a may be provided on any of the remaining circuits illustrated in this application for supplying the anode current to the tube I. It is apparent that the two secondary windings 9 and 9a are equivalent to a single secondary winding with an intermediate tap connected to the cathode circuit, and a single tapped secondary may be employed, if desired. 'Ihe operation of Figure 8 is the same as the operation of Figure 4.

In Figure 9, I have shown the circuit o1' Figure 4 applied to a system for indicating the weight of objects. Inthis arrangement, the condenser I 2a-I2h shown in Figure 4 takes the form of a capacity scale I3 comprising a ilxed plate Ila and a movable plate I3b suspended above the fixed plate by a spring I3c from a suitable support. The object I4 to be weighed is placed upon movable plate I3, and depresses this plate to a greater or less extent toward plate I3a, and thereby changes the value of its capacity in accordance with the weight oi' the object. An electric meter M is inserted in the anode circuit with tube I, and the scale of this meter may be graduated to indicate weight in pounds or any other desirable unit. The meter M may be located at a point remote from the weighing scale I3. The movable plate I3b may be arranged below the xed plate I3a, and the calibration of the meter M changed accordingly. Figure 9 also includes a separate secondary winding 8a for supplying space current to the anode circuit as in Figure 8. It is apparent that condenser 8 in Figure 9, and also in Figures 4, 5 and 6, may be included in the circuit at the upper end of secondary winding 8, if desired, as` shown in Figure 8.

Any of the circuits shown in Figures 2, 4 to 6 and 8 may be employed for the purpose of detecting the passage of persons or objects along a passageway by forming the condenser plates I2a-I2b of suitable size arranged on opposite sides of the passageway. The passage of a person or an object. such as an automobile, between respondingly.

-the changes in anode current.

the fixed plates will vary the capacity of the condenser and cause the anode current to vary cor- The variation in anode current may be utilized through well known means for indicating or recording the number of passages taking place, or for indicating the presence oi an object at a certain point in the passageway. The indicating device may be located at a. point remote from the control tube. The circuits o! Figures 1, 3 and 7 may also be used for the purpose'indicated above, by arranging the capacity elements I8 or I8a adjacent the passageway.

The circuit arrangements shown in Figures 2, 4 to 6 and 8 may be employed for detecting changes in characteristics of various materials in manufacturing processes by passing the material between the condenser plates I 2a-I2b, and the resulting changes in capacity of the condenser are reflected in the output circuit. For example, the presence of small metal particles or foreign substances in chewing gum and candy may be detected by passing the gum or candy between the condenser plates in a thin layer and noting These circuits may also be employed for detecting breaks in the manufacture of paper by passing the paper between the condenser plates, and the change in the dielectric constant of the condenser produced by a break in the paper will produce a change in the anode current sufficient to operate a suitable signal. The circuits of Figures 1, 3 and 'I may also be employed for the purpose indicated above by passing the material between capacity elements I8 or I8a and a grounded plate or wire spaced from the capacity elements to form a con'- denser arrangement the capacity of which is varied by the material under test.

Figures i to 3 produce more of an on-and-ofi control than Figures 4 to 9, due to the iact that the control potential is 180 degrees out of phase with the anode potential. The circuits of Figures 4 to 9 may be adjusted so that the presence of an extraneous object merely changes the anode current from one value to another, or, in case external grids (or grids insulated from the space current discharge) are employed, it is possible, by adjusting the grid potential to a high value, to completely cut off the anode current, and at this point the tube is quite sensitive to small changes in grid voltage, only a small decrease in grid voltage being suiiicient to allow an apprem cible current to iiow in the anode circuit. By adjusting the value of condenser II in Figure 2, or by adjusting the grid contact on resistance I in Figures 4 and 8, it is possible to operate these circuits so that the presence of the object I9 between the condenser plates I2a|2b merely reduces the anode current from one value to another, or the adjustment may be such as to cause the anode current to be completely cut off by the presence of object I9.

In Figures 1 to 3 the grid voltage is opposite in phase to the anode voltage, but in Figures 4 to 9 the grid voltage lags behind the anode voltage by an angle less than 180 degrees. The amount of lag depends upon the operation desired, but the circuits will operate with a lag varying from a few degrees to 180 degrees. I prefer, however, to operate between the range of 90 degrees and 180 degrees, since in this range a wider variation of anode current is obtained. It will also be noted that the phase relation between the grid and anode voltages remains xed in all circuits of my invention, and the relay is controlled by variation in magnitude of the control voltages.

While I have illustrated by invention as employing a gaseous relay tube having a heated electron emitting cathode, it will be understood that gaseous relays having other types of cathodes may be employed, ior example, I may use a. gaseous relay oi known type having a cold cathode and a keep-alive electrode for maintaining the gaseous atmosphere ionized. Also, instead of using a heated cathode of the type illustrated. the wellknown mercury pool cathode may be employed with a. keep-alive circuit.

Many modifications can be made in the circuit arrangements disclosed herein without departing from my invention. For example, in Figures 1 vand 2, and also Figures 4, 5, 6, 'I and 9, the condenser II, or the condenser 8, may be omitted in case there is sufllclent capacity existing between the winding 9 and the cathode winding 5 to serve the function of the omitted condenser. In

this case the lower terminal of winding 9 will remain free and disconnected. Also, the phase determining condenser 8 in Figures 4 to 9 may be inserted in the primary circuit of the grid transformer instead of in the secondary circuit as shown, and a separate transformer may be employed for supplying heating current to the cathode.

In the appended claims, the term lagging is to be interpreted to cover any lagging phase from a few degrees to 180 degrees. Also, the term signal device is intended to cover audible and visual indicators as well as recording and counting devices. The term thermionic valve is to be interpreted broadly to cover any of the various types of gaseous relay described herein.

What I claim is:

. 1. Electrical apparatus comprising a source of alternating electric current, a transformer the primary of which is connected to said source and having two secondaries, a thermionic valve the filament of which is connected across one of said secondaries, connections from the other secondary to the grid and plate of said valve, a condenser in the connection between the second secondary and the grid of said Valve, and means varying the capacity of said condenser and arranged to be actuated by an extraneous object.

2. Electrical apparatus comprising a source of alternating electric current, a transformer the primary of which is connected to said source and having two secondaries, a thermionic valve the filament of which is connected across one of said secondaries, connections from the other secondary to the grid and plate of said valve, a condenser in the connection between the second secondary and the grid of said valve, and means moving one of the plates of said condenser to vary the capacity of said condenser, said movement being controlled by an extraneous object.

3. A circuit comprising a source of alternating electrical energy, a transformer having a primary connected to said source, and two secondaries, a thermionic valve having its lament connected to one of said secondaries, a resistance element connected in parallel with a portion of the secondvsecondary an adjustable connection from said resistance element including a variable condenser and connected to the grid of said valve, and a connection from one end of the second secondary to the plate of said valve including a device to be actuated by current passing through said connection.

4. A circuit comprising a source of alternating electrical energy, a transformer having a primary connected to said source and two secondaries, a

thermionic valve having its filament connected to one of said secondaries, a resistance element connected in parallel with a portion of the second secondary, an adjustable connection from said resistance element including a condenser and connected to the grid of said valve, a connection from one end of the second secondary to the plate of said valve including a device to be actuated by current passing through said connection, and means for conducting current from the grid of said valve.

5. In combination, a source of alternating current, a gaseous relay device having a cathode an anode and a control electrode, a work circuit including said source and the space current path of said device, a signal device included in said work circuit, said gaseous relay having a characteristic such that plate current is cut oiI at a certain value of negative voltage on the control electrode and the arc discharge is established at a lower negative control voltage, means for supplying to said control electrode an alternating voltage opposite in phase with respect to said anode and` of suflicient magnitude to normally prevent current from cwing in said Work circuit, and a capacity element connected to said control electrode and being operative upon the approach of a conducting body in proximity thereto to reduce the voltage applied to said control electrode to a value to establish a discharge in said relay and therebyeiect energization of said signal device.

6. In an electric control system, the combination of a source of alternating current, a vapor electric device having a cathode and an anode enclosed within an insulating envelope, and a control electrode external of said envelope, a Work circuit including said source and the space current path of said device, a signal device included in said work circuit, said gaseous relay having a characteristic such that plate current is cut oi at a certain value of negative voltage on the control electrode and the arc discharge is established at a. lower negative control voltage, means for supplying to said external control electrode an alternating voltage opposite in phase with respect to said anode and of sufiicient magnitude to normally prevent current from flowing in said work circuit, and a capacity element connected to said control electrode and being operative upon the approach of a conducting body in proximity thereto to reduce the voltage applied to said control electrode to a value to establish a discharge in said relay and thereby effect energization of said signal device.

7. In combination, a source of alternating current, an arc discharge device having a cathode an anode and a control electrode, a work circuit including said source and the space current path of said device, a signal device included in said work circuit, said gaseous relay having a characteristic such that plate current is cut oil? at a certain value of negative voltage on the control electrode and the arc discharge is established at a lower negative control voltage, a transformer connected to said source and having a secondary winding for supplying to said control electrode an alternating voltage substantially opposite in phase with respect to said anode, means for adjusting the magnitude of the grid voltage to normally prevent current from iiowing in said work circuit, and a capacity element connected to said control electrode and being operative upon the approach of a conducting body in proximity thereto to reduce the voltage applied to said control electrode to a value to establish a discharge in said relay and thereby effect energization of said signal device.

8. In combination, a source of alternating current, a gaseous relay device having a cathode an anode and a control electrode, a work circuit including said source and the space current path of said device, a signal device included in said work circuit, said gaseous relay having a characteristic such that plate current is cut of! at a certain value of negative voltage on the control electrode and the arc discharge is established at a lower negative control voltage, means for supplying to said control electrode an alternating voltage of xed lagging phase with respect to the voltage of said anode, means for adjusting the amplitude of the control voltage, and a capacity element connected to said control electrode and being operative upon the approach oi' a conducting body in proximity thereto to change the amplitude of the voltage applied to said control electrode while maintaining the phase thereof substantially unchanged and thereby effect operation of said signal device.

9. In combination, a source of alternating current, a gaseous relay device having a cathode an anode and a control electrode, a work circuit including said source and the space current path of said device, a signal device included in said work circuit, means for supplying to said control electrode an alternating voltage lagging in phase with respect to the voltage of said anode, means for adjusting the amplitude of the control voltage, and a condenser connected between the control electrode and the cathode, said condenser being arranged to have its capacity varied by an extraneous object passing between its plates.

10. In combination, a source of alternating current, a gaseous relay device having a cathode an anode and a control electrode, a work circuit including said source and the space current path of said device, a signal device included in said work circuit, a condenser for connecting said control electrode to a source of alternating voltage lagging in phase with respect to the voltage of said anode, means for adjusting the amplitude of the voltage applied to said control electrode through said condenser, said condenser being arranged to have its capacity varied by an extraneous object passing between its plates.

11. In combination, a source of alternating current, a gaseous relay device having a cathode and an anode enclosed within an envelope and a control electrode located externally of the envelope, a work circuit including said source and the space current path of said relay, a signal device included in said work circuit, a transformer connected to said source and having a secondary winding, circuit connections from said secondary winding for supplying to said control electrode a control potential whichis negative with respect to the anode potential, adjustable means in said connection for adjusting the value of said control potential to a point near the critical cut-of! value, and a capacity element connected to said control electrode and being operative upon the approach of a conducting body in proximity thereto to vary the potential applied to said grid without reversing the phase thereof.

PALMER. HUNT CRAIG. 

